LibGL+LibSoftGPU: Add GPU side shader infrastructure

This adds a shader class to LibSoftGPU and makes use of it when linking
GLSL program in LibGL. Also adds actual rendering code to the shader
tests.

Userland/Libraries/LibSoftGPU/Shader.h

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2022, Stephan Unverwerth <s.unverwerth@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibGPU/Shader.h>
+
+namespace SoftGPU {
+
+class Shader final : public GPU::Shader {
+public:
+    Shader(void const* ownership_token);
+};
+
+}